1. Field of Invention
This invention relates to semiconductor light emitting devices including a wavelength-converting material and a filter material.
2. Description of Related Art
The color of light emitted from a semiconductor light emitting device chip such as a light emitting diode may be altered by placing a wavelength-converting material in the path of the light exiting the chip. The wavelength-converting material may be, for example, a phosphor. Phosphors are luminescent materials that can absorb an excitation energy (usually radiation energy) and store this energy for a period of time. The stored energy is then emitted as radiation of a different energy than the initial excitation energy. For example, xe2x80x9cdown-conversionxe2x80x9d refers to a situation where the emitted radiation has less quantum energy than the initial excitation radiation. The energy wavelength effectively increases, shifting the color of the light towards red.
If some light emitted from the chip is not absorbed by the phosphor, the unconverted light emitted from the chip mixes with the light emitted from the phosphor, producing a color between the color of the light emitted from the chip and the color of the light emitted from the phosphor. When used in applications requiring a particular color, the color of light emitted from the chip and the amount of light converted by the phosphor must be tightly controlled.
In accordance with embodiments of the invention, a light emitting device includes a semiconductor light emitting device chip having a top surface and a side surface, a wavelength-converting material overlying at least a portion of the top surface and the side surface of the chip, and a filter material overlying the wavelength-converting material. The chip is capable of emitting light of a first wavelength, the wavelength-converting material is capable of absorbing light of the first wavelength and emitting light of a second wavelength, and the filter material is capable of absorbing light of the first wavelength. In other embodiments, a light emitting device includes a filter material capable of reflecting light of a first wavelength and transmitting light of a second wavelength.
The filter material prevents at least a portion of light emitted from the chip that is unconverted by the wavelength-converting material from escaping the device. Use of the filter material may increase the color purity and lumen output of a wavelength converted semiconductor light emitting device.